There are systems, such as synchronous motors and generators, which supply electrical current to a rotor winding by way of slip rings. The current is typically applied to the slip rings via brushes mounted on a fixed conducting ring. Ordinarily, the slip rings in such systems are at low voltage. Some high voltage systems also employ slip rings for such purposes as power transfer. See, in this regard, U.S. Pat. No. 3,471,708 to Rauhut for a rotary transformer for coupling multiphase systems having a small frequency difference.
The brushes and brush-related components of such systems have many corners and edges that tend to create high electrical stresses in the surrounding air dielectric under high voltage conditions. These features can cause partial discharges that are deleterious to the operation of the system.
What is needed, therefore, and an object of the present invention, is a high voltage electrical system which provides an improved way of mounting slip ring-contacting members such as carbon brushes, for example.
An electrical current collector system comprises a rotatable shaft having at least one and preferably plural electrically conductive slip rings mounted thereon. For each phase, a slip ring is paired with a fixed conducting ring assembly. The fixed conducting ring assembly forms an envelope within which slip ring-contacting members are situated. The slip ring-contacting members can take many forms, including brushes (e.g., carbon brushes or metallic brushes) or rollers.
The fixed conducting ring assembly comprises a first conducting plate and a second conducting plate positioned parallel to one another to form a conductive ring channel therebetween. The slip ring-contacting members are mounted in the conductive ring channel. At least some of the slip ring-contacting members are mounted on the first conducting plate, others of the slip-ring contacting members are mounted on the second conducting plate. The slip ring-contacting members are preferably mounted in pairs in the fixed conducting ring assembly, one slip ring-contacting member of each pair being mounted on the first conducting plate and another slip ring-contacting member of each pair being mounted on the second conducting plate.
A wall extends between the first conductive plate and the second conductive plate of the fixed conducting ring assembly to further define the conductive ring channel. At least a portion of the wall is formed from a transparent material to permit visual inspection of the slip ring-contacting members.
An air flow gap is preferably provided between the slip ring and the fixed conducting ring assembly. Portions of the slip ring-contacting members extending into the gap to make electrical contact with the slip ring.
The envelope acts as an electrostatic shield or Faraday cage. The envelope is a high voltage envelope which puts the slip ring-contacting members and other components within the envelope at a same high voltage as the fixed conducting ring assembly.
Each pair of fixed conducting ring assembly and slip ring is substantially enclosed in its own grounded compartment for providing electromagnetic shielding. In one embodiment, an air buffer or the like is provided between the grounded compartments, e.g., the grounded compartments are phase isolated.
In one example deployment, the fixed conducting ring assembly is utilized in a rotating transformer system wherein the electrical current collector system applies current to a rotor assembly having rotor windings which rotates about the rotatable shaft, and wherein a stator has stator windings, and a motor is provided for rotating the rotor assembly.